respiration in plants · respiration in plants two most important prerequisites of life are...

MODULE - 2Forms and Function of

Plants and Animals

255BIOLOGY

Notes

Respiration in Plants

Two most important prerequisites of life are continuous supply of materials for

growth of body and energy for carrying out various life processes. All systems, from

cell to ecosystem, require energy to work. As you have already studied, light energy

is converted into chemical energy by plants during photosynthesis and this energy

is then stored in the bonds of complex molecules such as glucose, starch etc. It

is these complex molecules which are given the name ‘food’.

However, the energy in the food has to be made available to the cells in a usable

form. This is the role of respiration. Respiration is the process by which energy

in organic molecules is released by oxidation. This energy is made available to the

living cells in the form of ATP (Adenosine Tri-Phosphate). The O2 required for

respiration is obtained from the atmosphere. ATP is the energy currency of the cell.

This lesson covers various aspects of respiration in plants.

OBJECTIVES

After completing this lesson, you will be able to :

l define respiration, fermentation, photorespiration and respiratory quotient;

l list the basic events of anaerobic respiration and write the chemical equation

representing it;

l state the role of fermentation in industry;

l compare aerobic and anaerobic respiration;

l draw the flow chart to show the basic steps in Kreb’s cycle;

l explain how actually energy is released and stored in the form of ATP in the

cell;

l account for 38 ATP molecules that are released during aerobic respiration;

l list the factors that influence the rate of respiration and appreciate the

usefulness of RQ value of different food items.

12

RESPIRATION IN PLANTS

Dr.Megha Ghosal Osmania University / Dept. Of Biological Science 2015-2017

Dr.Megha Ghosal

BIOLOGY


Plants and Animals

256

Notes


12.1 RESPIRATION

Respiration is the stepwise oxidation of complex organic molecules and release of

energy as ATP for various cellular metabolic activities. Respiration involves

exchange of gases between the organism and the external environment. The plants

obtain oxygen from their environment and return carbon dioxide and water vapour

into it. This mere exchange of gases is known as external respiration or breathing

in case of animals. It is a physical process.

The biochemical process, which occurs within cells and oxidises food to obtain

energy, is known as cellular respiration. Various enzymes (biocatalysts) catalyze

this process. The process by which cells obtain energy from complex food

molecules depends upon whether or not oxygen is present in their environment and

utilised. Respiration is termed aerobic when oxygen is utilized and anaerobic when

oxygen is not utilized. In anaerobic respiration, organic molecules are incompletely

broken down in the cytosol of the cell and only a small fraction of energy is captured

as ATP for use by the cell. In aerobic respiration the reactions of anaerobic

respiration are followed by an oxygen requiring process that releases much larger

quantity of energy in the form of ATP. This occurs in the mitochondria of the

eukaryotes and in the plasma membrane of the prokaryotes.

It is important for you to note that many common processes occur in both, anaerobic

and aerobic respiration, such as,

l Oxidation reaction to release chemical energy from complex food.

l Use of coenzyme as carriers of hydrogen to remove the hydrogen from the

organic molecule leading to reduction of the coenzyme and oxidation of the

substrate. Most of the hydrogen carriers are NAD (nicotinamide adenine

dinucleotide) and FAD (flavin adenine dinucleotide).These are later reoxidised,

releasing energy for ATP synthesis

l Use of high-energy phosphate compounds like ATP for energy transfer.

The basic differences between the two forms of respiration are given in the

following table 12.1.

Table 12.1 Differences between aerobic and anaerobic respiration.

Aerobic (Aero = Air) Anaerobic (Anaero = No Air)

1. Takes place in presece of oxygen.

2. Leads to complete oxidation of

organic substrate.

3. It is most common in higher

organisms (both plants and animals).

1. Takes place in complete absence of

oxygen.

2. Incomplete oxidation of organic

substrate takes place.

3. Takes place in lower organisms

such as bacteria, fungi, and in higher

animals under limiting conditions

of oxygen (e.g. in muscles when

oxygen present is insufficient).

Dr.Megha Ghosal

Dr.Megha Ghosal


Plants and Animals

257BIOLOGY

Notes


4. C6H12O6 → 6CO2 + 6H2O

+ 6O2 +38 ATP

5. Takes place in the cytoplasm, and

mitochondria in eukaryotes and

plasma membrane in prokaryotes.

Coenzyme is a complex non-protein molecule which is temporarily bound

to an enzyme and acts as a link between metabolic pathways, (series of

biochemical reactions).

INTEXT QUESTIONS 12.1

1. How do plant and other organisms obstain energy for various activites such as

growth?

............................................................................................................................

2. Name the energy rich molecule formed during respiration from food.

............................................................................................................................

3. Give two differences between aerobic and anaerobic respiration.

............................................................................................................................

12.2 EXTERNAL RESPIRATION/GASEOUS EXCHANGE

l In plants, the atmospheric air moves in and out by simple diffusion that takes

place through,

(a) the general body surface of the plant (stems, roots, fruits and seeds);

(b) lenticels (openings in the bark of the tree trunk (Fig. 12.1);

(c) stomata present in the leaves and young stems.

Fig. 12.1 Lenticels on the bark of a tree

4. C6H12O6 → 2Ethyl alcohol +

2CO2 +2 ATP

(as in yeast)

OR

C6H12O6 → 2 Lactic acid + 2 ATP

(as in muscles)

5. Takes place in the cytoplasm.

Dr.Megha Ghosal

Dr.Megha Ghosal

BIOLOGY


Plants and Animals

258

Notes


l Plants do not need O2 carrier (in contrast to animals) where O2 is carried by

blood). This is because O2 requirement is less than in animals and plants have

a large surface area (leaves) to absorb the required amount of O2 through

diffusion.

l From the atmosphere gases enter the intercellular spaces inside the plants. As

O2 is utilized, more of it diffuses into the plant. Since CO2 is being continuously

formed, its concentration result in tissue spaces becomes higher than in the

surrounding air. As a result, it diffuses out of the plant, specially when it is

being used for photosynthesis.

l Can you explain why during the day, plants give out O2 instead of taking it

up for respiration?

In plants, O2 released during photosynthesis in day time is made available for

respiration. However, rate of photosynthesis is greater than that of respiratin. Thus,

plants give out excess O2 in the daytime. However, they give out only CO2 at night

as photosynthesis stops in the absence of sunlight. Animals give out CO2 at all

times.


1. Name the surfaces that help plants in taking up oxygen from the atmosphere.

............................................................................................................................

2. Name the process by which oxygen is taken up by the plants from the

atmosphere.

............................................................................................................................

3. Name the gases given out by plants during daytime and night.

............................................................................................................................

4. Why do plants not have any special respiratory organs like animals? Give two

reasons.

............................................................................................................................

12.3 CELLULAR RESPRIATION

Oxygen that is absorbed is used to oxidize the nutrients, viz., glucose, amino acids

and fatty acids completely producing CO2, water and energy. It occurs within the

cells and tissues. Observe the figure 12.2 and identify the steps of cellular (aerobic

and anaerobic) respiration. Note that the first stage in all these pathways is

glycolysis.

Dr.Megha Ghosal

Dr.Megha Ghosal


Plants and Animals

259BIOLOGY

Notes


Fig. 12.2 Pathways in cellular respiration

12.3.1 Glycolysis (Also known as Embden Meyerhof Parnas Pathway)

Whether or not oxygen is available in the cells, the breakdown of glucose is initially

always anaerobic. It is common to both aerobic and anaerobic respirations.

It involves oxidising glucose (6-carbon compound) to two molecules of pyruvic

acid through a series of enzymatically controlled reactions occuring in the cytosol.

Initial substrate is glucose (either from photosynthesis as in plants or from

carbohydrate digestion as in animals).

Glycolysis may be subdivided into 3 major phases:

1. Phosphorylation of glucose to fructose 1,6 diphosphate. This is activation of

glucose and 2ATPs are used.

2. Splitting of this compound into two 3- carbon sugar phosphates, which are

interconvertible. Note that this is the origin of the term glycolysis meaning

splitting of glucose.

3. Oxidation by dehydrogenation. Each 3-C sugar phosphate is oxidized by

removal of hydrogen, making a reduced NAD that is NADH and production

of 2ATPs.

This group of reactions is believed to be one of the first energy capturing

reactions which evolved about three billion years ago in ancient bacteria

and today it occurs in virtually all cells of all forms of life.

ATP → ADP + Pi + 30.6 kJ

Lactate

(lactic acid)

ethanol + CO2

Sugar (6C)

Glycolysis

Krebs’

cycle

2 × pyruvate (3C)

Dr.Megha Ghosal

Dr.Megha Ghosal

BIOLOGY


Plants and Animals

260

Notes


The balanced equation is:

l Glucose + 4ADP + 4Pi + 2NAD → 2Pyruvic acid + 4ATP + 2NADH

l Two molecules of ATP were used up in the initial steps of glycolysis. Thus,

the net gain of ATP during glycolysis is 4 – 2 = 2 ATP. Also, 2NADH + H+

are produced.

l Thus, we see that only a small amount of energy is released at the end of

glycolsis.

12.3.2 Fermentation

Further oxidation of Pyruvic acid requires O2 (as you will study soon). It then enters

mitochondria for aerobic respiration.

Under anaerobic conditions (or insufficient supply of O2) microbes and plants carry

out fermentation.

Fermentation involves reduction of pyruvic acid to ethyl alcohol and CO2 (as in

yeast) or to lactic acid (as in muscle cells of animals) and oxidation of NADH

to NAD+. Thus, NAD is regenerated which can be used in glycolytic pathway and

production of 2 ATPs can continue under anaerobic conditions. (Refer to the figure

12.3). Note that there is no further release of ATP during fermentation.

Although you are more familiar with the term fermentation in context with

alcoholic fermentation it is now being used for the anaerobic pathway

followed by pyruvic acid.

Dr.Megha Ghosal

Dr.Megha Ghosal


Plants and Animals

261BIOLOGY

Notes


Fig. 12.3 Pathways of anaerobic respiration

Significance of fermentation

Fermentation has a number of industrial applications. It is made use of on a large

scale in certain industries. Microorganisms like the different strains of bacteria and

yeast are cultured in very large numbers and used for various purposes.

1. In bakeries for preparing bread, cakes and biscuits etc.

2. In breweries for preparing wine and other alcoholic drinks.

3. In producing vinegar and in the tanning and curing of leather.

4. Ethanol is used to make gasohol, a fuel that is used for cars in Brazil.

5. In everyday life, fermentation is used while making idli, dosa, bhatura, dhokla

etc. The kneaded flour or maida left for some hours in warm environment

becomes somewhat spongy (leavening). This is because of fermentation by the

bacteria that begin to grow in it. As carbon dioxide escapes, it causes leavening.

Fermentation products give a typical flavour and taste to these items.

Do you know why muscles pain during prolonged exercise? This is due

to accumulation of lactic acid.

12.3.3 Fate of pyruvic acid in aerobic respiration

l You have already learnt how glucose is converted into 2 molecules of pyruvic

acid in the cytoplasm of a cell during glycolysis.

Dr.Megha Ghosal

Dr.Megha Ghosal

BIOLOGY


Plants and Animals

262

Notes


l In presence of oxygen, pyruvic acid enters the mitochondria and is decarboxylated

(removal of CO2) and dehydrogenated (removal of H) to acetyl CoA. Acetyl

CoA is thus the connecting link between glycolysis and the next series of

reactions that yield more energy in the form of ATP. Acetyl CoA can also be

generated from fats and proteins.

Krebs’ citric acid cycle

l Acetyl CoA is the molecule entering the Krebs’ cycle taking place in the matrix

of the mitochondria.

l Details of this cycle were worked out by Sir Hans Krebs in the 1930s. It is

also known as tricarboxylic acid cycle or TCA cycle.

l Steps of the Krebs’ cycle are as follows, (See Fig. 12.4)

Fig. 12.4 Kreb’s cycle (simplified)

Summary of this phase in respiration is

2Pyruvic acid + 8NAD + 2FAD + 2ADP → 6CO2 + 8NADH + 2FADH2 + 2ATP

H-carrier NAD and FAD are derived from vitamin B complex and are

known as coenzymes

l Acetyl group (2 carbon) enters the cycle by combining with oxaloacetate (4

carbon), to form citrate (6 carbon). This initiates citric acid cycle.

l As acetyl group passes round the cycle, the 2 carbon atoms are lost in CO2 in

two decarboxylation reactions, and hydrogen is added to hydrogen carriers in

four dehydrogenation reactions, resulting in a total of 3 NADH2 and 1 FADH2molecules.

Dr.Megha Ghosal

Dr.Megha Ghosal


Plants and Animals

263BIOLOGY

Notes


l One molecule of ATP is also made directly for every turn of the cycle.

(Remember that two acetyl groups were made from one glucose molecule, so

two turns of the cycle occurs per glucose molecule used). Oxaloacetate is

regenerated at the end of the cycle ready to accept another acetyl group.

l Thus, at the end of the Citric Acid Cycle, there are a total of 10NADH and

2FADH2 (2NADH from glycolysis).

l Note that all the hydrogen from the original glucose is now on hydrogen carriers,

NAD and FAD.

These hydrogen carriers enter the next phase known as the respiratory chain for

further release of energy.

Respiratory Chain or Electron Transport Chain (E.T.C.)

l The hydrogen carriers now move to the inner membrane of the mitochondrion.

This membrane has folds called cristae, which increase its surface area.

l Hydrogen carried to the cristae undergoes stepwise oxidation using molecular

oxygen and energy is released in a series of small steps. Some of this energy

is used to make ATP from ADP and inorganic Phosphate (Pi). This is called

oxidative phosphorylation.

l During these reactions the hydrogen is split into H+ and electrons

(e–1), which are accepted by a series of hydrogen or electron carriers ending

with oxygen. This series of carriers constitute the respiratory chain (Fig. 12.5).

Fig 12.5 Respiratory Chain.

l Hydrogen or electrons at a higher energy level are passed from one carrier to

the next, moving downhill in energy terms, until they reach oxygen the final

acceptor of electrons which as a result is reduced to water.

l At each transfer some energy is released and in some of the transfers this is

used for the formation of ATP.

Dr.Megha Ghosal

Dr.Megha Ghosal

BIOLOGY


Plants and Animals

264

Notes


l The final step involves cytochrome oxidase enzyme, which hands over the

electrons to the H+ before being accepted by oxygen to form water.

l For each NADH2 that enters the respiratory chain, 3 ATP can be made but for

each FADH2, only 2 ATP can be made. Can you guess why? Because FADH2enters the respiratory chain at a lower level in the chain of reactions.

Substances like carbon monoxide and H2S act as poisons because they block

the H-transfer system and stops ATP generation.

Overall budget for aerobic respiration of one glucose molecule

See table no: 12.2

CO2 ATP NADH+H+ FADH2

Glucolysis - 2 2 -

Pyruvate-> Acetyl coA 2 - 2 -

Krebs cycle 4 2 6 2

Total 6CO2 4ATP 10 NADH+H+ 2 FADH2

10×3=30 ATP 2×2=4 ATP

Total No. of ATP mols = 38

* Remember that two turns of the cycle take place per glucose molecule as at

the end of glycolysis two pyruvic acid molecules are formed each of which

separately enters the Krebs’ cycle.

Fig 12.6 Summary of Aerobic respiration.

Dr.Megha Ghosal

Dr.Megha Ghosal


Plants and Animals

265BIOLOGY

Notes


12.3.4. Significance of Krebs’ cycle and Acetyl CoA

1. It is the major pathway to release reduced coenzymes and energy in a controlled

manner.

2. It is the common pathway for oxidative breakdown of CHO, fatty acids and

amino acids. Fatty acids undergo β oxidation to produce acetylCoA and amino acids from proteins enter Krebs’ cycle after deamination

(removal of –NH2 group) of amino acids.

3. Krebs’ cycle provides many intermediate compounds needed for the synthesis

of other biomolecules like amino acids, nucleotides, chlorophyll, fats, etc.


1. Why is pyruvic acid converted into alcohol or lactic acid during fermentation?

............................................................................................................................

2. Why is there less release of energy during anaerobic respiration?

............................................................................................................................

3. List the three phases of aerobic respiration of glucose. Where in the cell do

these reactions take place?

............................................................................................................................

4. What is the role of O2 in aerobic respiration?

............................................................................................................................

5. Name the substrate and product of Krebs’ cycle.

............................................................................................................................

6. How do fatty acids enter Krebs’ cycle?

............................................................................................................................

12.4 RATE OF RESPIRATION AND FACTORS EFFECTING IT

The rate of respiration can be measured by the amount of CO2 released. The rate

of respiration varies in different organs and with age.

In general the factors which affect respiration include internal factors such as the

activity of the respiratory enzymes the type of substrate; and external factors such

as oxygen, water, temperature etc.

(a) Type of substrate-Respiratory substrate may be carbohydrate, protein or fats.

The kind of substrate being oxidized is obtained by measuring the respiratory

quotient. What is respiratory quotient or R.Q?

R.QVolume of CO evolved

Volume of O consumed

2

2

=

Dr.Megha Ghosal

Dr.Megha Ghosal

BIOLOGY


Plants and Animals

266

Notes


For carbohydrates, CO2/O2 = 1 as in stem and roots.

For protein, CO2/O2 < 1 as in protein rich seeds like pulses.

For fat and oils CO2/O2 > 1 as in oil containing seeds e.g. mustard.

As for fats RQ > 1 more energy is released per mol of fat than per mol

of glucose.

(b) Temperature - The temperature between 30-35°C is most suitable for respiration.

Can you guess why? The enzymes can work best in this range. Respiration is

reduced beyond 50°C and also at very low temperatures (0-10°C).

(c) Oxygen-the rate of respiration increases with rise in oxygen concentration. As

O2 concentration increases from zero, the rate of respiration increases. However,

beyond a limit the rate of increase falls.

(d) Carbon dioxide–rate of respiration decreases if CO2 is allowed to accumulate.

(e) Water–respiration is very slow if the water content of the protoplasm is low

as in dry, matured seeds. Dormant seeds show very low rate of respiration.


1. What is the R.Q. for carbohydrates and fats?

............................................................................................................................

2. What is the effect of high concentration of O2 on respiration?

............................................................................................................................

3. What is the ideal temperature for the process of respiration ?

............................................................................................................................

4. Define R.Q.

............................................................................................................................

12.5 PHOTORESPIRATION

l Your have aready studied that during dark reaction of photosynthesis, the

enzyme RUBISCO catalyses the carboxylation of RUBP :

RUBP + CO2 RUBISCO → 2PGA (Phosphoglyceraldehyde) → Calvin cycle

l This enzyme also has very high affinity for O2. It can therefore, catalyze the

reaction of O2 with RUBP (oxygenation).

Dr.Megha Ghosal

Dr.Megha Ghosal


Plants and Animals

267BIOLOGY

Notes


l The respiration that is initiated in chloroplast and occurs in presence of light

and high concentration of O2 (and low CO2) is called photorespiration :

RUBP + O2 RUBISCO → 2PGA + 1 Phosphoglycolate

↓ Calvin cycle

Thereafter, phosphoglycolate undergoes series of reaction in mitochondria and

peroxisomes. 2 molecules of phosphoglycolate ultimately produce 1 molecule of

PGA and 1 molecule of CO2. Note that there is no ATP production here, unlike

respiration.

l This occurs because RUBISCO anzyme has the same active site for both CO2and O2.

l Oxygenation of RUBP in presence of oxygen leads to a loss of about 25%

carbon fixed by plants during dark reaction.

l Use: Protects the plants from photo oxidative damage by utilising part of the

solar energy which would otherwise damage the plant pigments.


1. Name the products that are produced when RUBP combines with O2. Name

the enzyme that is responsible for this reaction.

............................................................................................................................

2. Give one point of difference between respiration and photorespiration.?

............................................................................................................................

3. State the conditions under which photorespiration occurs?

............................................................................................................................

Activity I

To demonstrate anaerobic respiration in germinating seeds

Take eight or ten soaked pea seeds with the seed coats removed and push them

into the mouth of a test tube filled with mercury and invert it in a beaker of mercury.

The pea seeds float on the top and are completely surrounded by mercury. After

about two days there is a fall in the level of the mercury because of gas liberation.

If potassium hydroxide (KOH) is introduced into the test tube then it is found that

KOH floats up through the mercury and on coming in contact with the gas, makes

the level of mercury to rise up again. How can you say why does this happen? KOH

Dr.Megha Ghosal

Dr.Megha Ghosal

BIOLOGY


Plants and Animals

268

Notes


absorbs the carbon dioxide gas liberated by the seeds. How this experiment

demonstrates anaerobic respiration (See Fig. 12.7)

Fig. 12.7 Anaerobic respiration in germinating seeds

Activity II

Anaerobic respiration in yeast

Procedure : Take a pinch of dry baker’s yeast (in water) or few mL of yeast

suspension used in a bakery. Add this in 10 mL of 10% glucose solution in test

tube A. Cover the surface of the liquid in the tube with oil to prevent contact with

air. Close the test-tube tightly with a cork. Take a double bent glass delivery tube

with one end small and other end long (See Fig. 12.8).

Fig. 12.8 Anaerobic respiration in yeast.

Insert the short end through the rubber-cork stopper so that it reaches the air inside

the tube A. Insert the other end of the tube into the limewater containing test tube

B, as shown in the figure.

Dr.Megha Ghosal

Dr.Megha Ghosal


Plants and Animals

269BIOLOGY

Notes


Place test tube A in warm water 37-38°C in a beaker. Observe that lime water

gradually turns milky indicating evolution of CO2 from yeast preparation. Also note

that the level of the limewater in the delivery tube does not rise, showing that there

is no fall in volume of gas in test tube A and therefore no utilization of O2 by yeast.

Keep the experimental set up for one day. Open the stopper of tube A and smell.

Do you notice the smell of alcohol? Can you name the alcohol and write the

equation for the alcoholic fermentation

C6H12O6 → 2C2H5OH + 2CO2 + 2ATP

Activity III

You can use similar set-up as in activity II to demonstrate aerobic respiration in

yeast. Make the following changes :

1. Replace the test tube A with a large conical flask so that it has sufficient space

left above the glucose solution with yeast.

2. The surface of the solution should not be covered with oil to permit easy contact

with air.

3. Observe that lime water turns milky in this experiment too, indicating evolution

of CO2. Also note that the level of H2O in the delivery tube B also rises

indicating a fall in gas volume in tube A. how do you explain this? Oxygen

is utilized by the yeast, you will not smell alcohol after the reaction in test

tube A

Note that yeast grows both in aerobic and anaerobic conditions but better under

aerobic conditions. The secret of brewing is to regulate the conditions very strictly

WHAT YOU HAVE LEARNT

l All living organisms require energy. Oxidation of food molecules provide this

energy.

l Respiration involves (i) external respiration or gaseous exchange, and

(ii) cellular respiration.

l Anaerobic respiration is the process of incomplete oxidation and produces only

2 molecules of ATP whereas aerobic respiration is a process of complete

oxidatin with production of 38 molecules of ATP.

l Aerobic respiration occurs in three main steps viz. Glycolsis; Krebs’ cycle;

electron trasport chains.

l Steps of glycolysis are common between aerobic and anaerobic respiration.

l Glycolysis occurs in cytoplasm and Krebs’ cycle and ETC in mitochondria.

l Alcoholic fermentation has many industrial applications.

l Young parts of the plants show higher rate of respiration.

Dr.Megha Ghosal

Dr.Megha Ghosal

BIOLOGY


Plants and Animals

270

Notes


l Factors like type of substrate, temperature, oxygen and amount of available

water influences the rate of respiration.

l RQ value is important in identifing the kind of substrate used in respiration.

l Photorespiration occurs in plants during intense light and low level of carbon

dioxide. There is no net gain of ATP. It protects the chlorophyll pigments from

photo-oxidation.

TERMINAL EXERCISES

1. Define respiration

2. What is the role of O2 in electron transport chain (ETC)?

3. How many molecules of ATP are released when glucose is oxidised to

(a) CO2 and H2O?

(b) Ethyl alcohol and CO2?

4. Write the equation for aerobic respiration.

5. Name the end product of electron transport chains.

6. Respiration is a continuous process in plants. Then why is it that they give out

O2 and not CO2 during the day?

7. What is the site for

(a) Glycolysis,

(b) Krebs cycle,

(c) ATP generation by oxidative phosphorylation?

8. What is the fate of pyruvic acid in (a) presence, and (b) absence of oxygen?

Write the equations representing the processes.

9. What is the significance of stepwise oxidation of organic molecules instead of

one step reaction?

10. What is the significance of photorespiration?

11. List the substrates that enter and the products produced in

(a) Glycolysis

(b) Krebs cycle

12. How is yeast useful in industry? Give any three examples.

13. How does exchange of respiratory gases take place in plants

14. Define RQ. What is its significance?

15. Mention the significance of TCA cycle.

16. Why does fermentation yield less energy than aerobic respiration?

Dr.Megha Ghosal

Dr.Megha Ghosal


Plants and Animals

271BIOLOGY

Notes


17. List any 2 important contributions of PPP in a cell.

18. What are the three major phases of glycolysis?

19. What is the importance of Krebs’ cycle?

20. Differentiate between aerobic and anaerobic respiration

21. Why is photorespiration a wasteful reaction?

22. What is respiratory chain or ETC? What is its significance?

ANSWERS TO INTEXT QUESTIONS

12.1 1. Plants covert solar energy to chemical energy and store it in the form of

complex organic molecules. During respiration, they are oxidised and

large amount of energy is released. This is stored as ATP. Plants use this

ATP for metabolic activities.

2. In the form of ATP

3. Please see text.

12.2 1. Gaseous exchange takes place through the general body surface of the

plants; through the stomata; the lenticels.

2. Diffusion

3. Oxygen; carbon dioxide

4. (a) They have a large surface area to exchange gases from & (b) their

requirement of oxygen is much less.

12.3 1. In presence of O2, it is completely broken down to simple forms such

as CO2 and H2O.

2Pyruvic acid + 6O2 → 6CO2 + 6H2O + 30ATP

(8ATP are obtained from glycolysis)

In absence of O2 they carry out alcoholic fermentation.

2Pyruvic acid → 2Ethyl alcohol + 2CO2

2. This is becausse organic molecules are only partially oxidised in anaerobic

respiration and much of the energy remains in the end products such as

alcohol or lactic acid.

3. Glycolysis-in cytosol

Krebs’ cycle-matrix of mitochondria

E.T.C.-inner membrane of mitochondria

Dr.Megha Ghosal

Dr.Megha Ghosal

BIOLOGY


Plants and Animals

272

Notes


4. O2 acts as the terminal acceptor of H2, removed from the glucose molecule

and gets reduced to H2O.

6. Substrate- Acetyl CoA

Product-2 CO2, 3 NADH, 1 FADH2, 1 ATP

7. Fatty Acid undergo β oxidation and produce acetyl CoA. This can enter theKreb’s cycle

12.4 1. R.Q. is 1

2. Rate of respiration increases up to a point and beyond this point its rate of

increase falls.

3. 30-35°C

4. It is the ratio of the volume of CO2 evolved to the volume of O2 consumed

in respiration. It gives us an idea of the kind of substrate used for

respiration.

12.5 1. Products are1 P.G.A. and 1 Phosphoglycolate

2. Respiration Photorespiration

1. Occurs in mitochondria 1. It involves 3 organelles

chloroplast, mitochondria

peroxisome

2. Substrate is glucose 2. Substrate is RUBP

3. ATP, CO2 and H2O are 3. The products are only CO and

given out as products P.G.A. and no ATP is generated

4. Takes place in both plants 4. Takes place in green plant (C3)

5. Occurs at both day and 5. Takes place under high O and

night low CO and high temperature.

Therefore occurs only during

the day.

6. Makes energy available 6. It is wasteful reaction. Its only

for metabolic activities. use is that it prevents

photooxidative damage to

the plants.

(any one)

3. (a) Light

(b) High concentration of O2

(c) Low concentration of CO2

Dr.Megha Ghosal Osmania University / Dept. of Biological Science 2015-2017

Dr.Megha Ghosal

respiration in plants · respiration in plants two most important prerequisites of life are...

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